What is the diagnosis for a patient with stool showing 3 nuclei, consistent with Entamoeba histolytica cysts?

Diagnosis: Entamoeba histolytica Cyst Carrier

The finding of cysts with 3 nuclei in stool is diagnostic of Entamoeba histolytica infection, specifically indicating the cyst stage of this pathogenic parasite. 1

Morphologic Identification

• Mature E. histolytica cysts characteristically contain 1-4 nuclei, with the presence of 3 nuclei representing a developing mature cyst form that is pathognomonic for this species 1
• This finding confirms intestinal colonization with E. histolytica, as cysts are the infective form passed in stool 1, 2
• Microscopic examination should ideally be performed within 15-30 minutes of stool passage for optimal identification, though cysts are more stable than trophozoites 3

Clinical Significance and Next Steps

Determine Disease Status

• You must now determine whether this patient is symptomatic or asymptomatic, as this fundamentally changes management 2
• If the patient has bloody diarrhea with severe abdominal pain but minimal or no fever, this strongly suggests invasive intestinal amebiasis requiring dual therapy 3
• If the patient is completely asymptomatic, they are a cyst carrier who still requires treatment to prevent progression to invasive disease and eliminate transmission risk 2

Symptomatic Disease Indicators

• Look specifically for: bloody stools (occurs in <15% but highly suggestive), severe cramping abdominal pain, tenesmus, and notably the absence or minimal presence of fever (only 8% have fever) 3
• Persistent diarrhea lasting ≥14 days is characteristic of amebic infection 3
• The classic triad of severe abdominal pain + bloody stools + minimal fever should immediately trigger treatment for invasive amebiasis 3

Treatment Algorithm

If Symptomatic (Invasive Disease)

• Requires tissue amebicide (metronidazole or tinidazole) followed by luminal amebicide (paromomycin) 2

If Asymptomatic (Cyst Carrier)

• Treat with paromomycin 30 mg/kg/day divided into 3 oral doses for 10 days (FDA-approved regimen) 2
• Alternative: diloxanide furoate 500 mg three times daily for 10 days (86% cure rate) 2
• Do NOT use metronidazole or tinidazole in asymptomatic carriers—these tissue amebicides are only for invasive disease 2

Critical Pitfalls to Avoid

• Do not confuse the 3 nuclei with 3 separate organisms or with leukocytes—this is a single cyst with multiple nuclei, which is the normal morphology of E. histolytica cysts 2
• Do not assume the patient needs reporting as a case of amebiasis if asymptomatic—asymptomatic cyst carriers should not be reported 1, 2
• If you order serology and it's positive in an asymptomatic person, do not interpret this as active extraintestinal disease—antibodies may persist from past infection 1
• Perform follow-up stool examination at least 14 days after completing treatment to confirm parasite elimination 2